(When the 'xml:space' attribute is not set to
'preserve', then)
Leading and trailing white space inside a block element must be
removed.

xhtml_conform-13

(When the 'xml:space' attribute is not set to
'preserve', then)
LINE FEED characters must be converted into one of the following
characters: a SPACE character, a ZERO WIDTH SPACE character
(&#x200B;), or no character (i.e. removed).

xhtml_conform-14

(When the 'xml:space' attribute is not set to
'preserve', then)
A sequence of white space characters without any LINE FEED
characters must be reduced to a single SPACE character.

xhtml_conform-15

(When the 'xml:space' attribute is not set to
'preserve', then)
A sequence of white space characters with one or more LINE FEED
characters must be reduced in the same way as a single LINE FEED
character.